Hello; You describe the noise and roughness pretty well, my guess would be the rear bearing. The Enya 46 is a pretty durable engine well worth saving. Take the front case off, the crank will stay with it, then you can push and turn the crank and feel for roughness, you will also be able to see the balls turn and look for rough spots. If you decide to replace the bearing (probably), just heat the front case in an oven and push the crank out then tap the case on a piece of hardwood, and if your lucky the bearing will fall out easily. The bearing might come out when you push the crank out. You don't have to touch the cams valves or head to do this. When you re-assemble the engine just make sure you index the crank pin with the cam shaft and don't damage any gaskets if there are any. Enya engines are a little different, but their construction makes this job much easier then Saito or OS in that you don't have to disturb the cam. You might ahve noticed that you can't remove the back cover, as it's the cam chest.